20mm ballast mate, 4-1 mix with cement, 10 inch deep all way round and make sure you screed it off right and have a slight slope for water.........aco drains, get the cheapest ones you can get, no need to get the heavy duty ones if not driving on them..........what are they going against??? if you can get the ballast picked up loose as you always get more for your money, which will be around £35 a tonne if you go to a builders merchants, or ring your local quarry/s to see if you can pick some up from there............